The central hypothesis for this grant is that interictal hypometabolism seen in epileptic human brain reflects impaired mitochondrial metabolism, on consequence of which is an alteration in glial glutamate metabolism,, especially glutamate uptake. The goal of this subsection is to test specific hypotheses regarding the functional consequences of these changes. using brain slices and cultured astrocytes. Tissue from patients as well as from chronically epileptic kainate-treated rats obtained from human tissue will be correlated with the data obtained in the other subprojects. In the first Specific Aim we will test the hypothesis that extracellular homeostasis is impaired in epileptic tissue. The regulation of [K+]o, the size of the extracellular space and extracellular pH will be assayed using ion-selective microelectrodes in human and rodent tissue. The effect of specific metabolic inhibitors on these variables will be examined. In the second Specific Aim we will examine if glutamate uptake impaired in epileptic tissues. The changes in glutamate and glutamine levels will be measured during synaptic and spontaneous activity and control tissue using HPLC of the extracellular fluid. This links directly with the microdialysis studies in the Core. The effects of glutamate uptake inhibitors on the amino acid concentrations and on seizure activity in both epileptic and control tissue will also be investigated. The third Specific Aim tests the hypothesis that an increase in extracellular glutamate associated with defective glutamate uptake acts to limit glutamate release via presynaptic mechanisms. Finally, confocal microscopy of glutamate- induced Ca2+ transients in cultured glia will be examined to test the hypothesis that elevated extracellular glutamate alters glial plasticity. Cultures from control and epileptic tissue will be used to assess whether epileptic tissue has comparable responses to that chronically exposed to glutamate. We hypothesize that this will be the condition found in tissue from the patients with impaired mitochondrial metabolism. These experiments will complement the other three projects by examining several possible functional consequences of impaired mitochondrial metabolism at the level of single neurons or glial cells.